When I got to the caption step on this article, the image preview element turned this strange color. The validation warning’s icon appeared on top of the message. And the visual treatment for a Visual Editor “table” appeared around the image preview.
And even after I saved the image (see second screenshot), the strange color remained in the article itself.
@Tgr This is probably a bug in the inserting logic, it puts the image inside the first non-template element with editable contents. I assumed that would be a paragraph, but apparently table cells match the condition as well.